xfrm: support 'multicast' attribute on interfaces

You shouldn't need the overhead of GRE just to add multicast
capability on a point-to-point interface (for instance, you might
want to run mDNS over IPsec transport connections, and Avahi
requires IFF_MULTICAST be set on interfaces, even point-to-point
ones).

Borrowed heavily from:

    b3c9321b9e gre: Support multicast configurable gre interfaces

Signed-off-by: Philip Prindeville <[email protected]>

package/network/config/xfrm/Makefile

@@ -2,7 +2,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=xfrm
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 PKG_LICENSE:=GPL-2.0
 
 include $(INCLUDE_DIR)/package.mk

package/network/config/xfrm/files/xfrm.sh

@@ -11,8 +11,8 @@ proto_xfrm_setup() {
 	local cfg="$1"
 	local mode="xfrm"
 
-	local tunlink ifid mtu zone
-	json_get_vars tunlink ifid mtu zone
+	local tunlink ifid mtu zone multicast
+	json_get_vars tunlink ifid mtu zone multicast
 
 	[ -z "$tunlink" ] && {
 		proto_notify_error "$cfg" NO_TUNLINK
@@ -36,6 +36,8 @@ proto_xfrm_setup() {
 
 	json_add_string link "$tunlink"
 
+	json_add_boolean multicast "${multicast:-1}"
+
 	json_add_object 'data'
 	[ -n "$ifid" ] && json_add_int ifid "$ifid"
 	json_close_object
@@ -61,6 +63,7 @@ proto_xfrm_init_config() {
 	proto_config_add_string "tunlink"
 	proto_config_add_string "zone"
 	proto_config_add_int "ifid"
+	proto_config_add_boolean "multicast"
 }